A Dunbarton woman is being treated at Dartmouth-Hitchcock Medical Center after being hit by a car while riding a bicycle on Clinton Street Thursday morning.

Susanne Kibler-Hacker, 42, was traveling eastbound on her commute to work when she was hit from behind. A hospital spokeswoman said last night she was listed in serious condition.

The police did not know the full extent of Kibler-Hacker's injuries, but Sgt. Jim Berry said they included a possible broken leg and dislocated tailbone.

The driver, a 50-year-old woman from Weare, was issued a warning to "exercise due care," Berry said. Speed and alcohol were not factors.

Kibler-Hacker is the vice president for development at the Society for the Protection of New Hampshire Forests, where she oversees fundraising and membership.

Jack Savage, spokesman for the Forest Society, could not speak to the specifics of her condition but acknowledged that Kibler-Hacker was injured and said that she frequently commutes to work by bike. Savage said she is the office coordinator for the state's ride-to-work days.

The crash highlights the challenges that state planners and cyclists face as they promote safe, alternative transportation.

Much of Clinton Street was recently repaved. A stretch east of the intersection with Silk Farm Road was redesigned with narrower travel lanes and wider shoulders to make way for cyclists. West of Silk Farm Road on Clinton Street, where Kibler-Hacker was struck, however, there was too little pavement to allow for wider shoulders, said Larry Keniston, the intermodal facilities engineer for the Department of Transportation.

The crash happened outside the home of Lindsay Goff, a nurse who said she assisted Kibler-Hacker afterward. She said the shoulder there is about a foot wide and the speed limit is 45 mph.

"I always say I think it's crazy that people ride bikes on this street," Goff said.

Goff estimated that Kibler-Hacker, who was wearing fluorescent clothing and a helmet, was thrown about 20 feet from where she was hit.

"Her back tire was torn off the bike and just in pieces," she said.

Goff said Kibler-Hacker was responsive and complaining of leg and back pain. She was taken to Concord Hospital and then transferred to Dartmouth.

Keniston said it's important for cyclists to have a plan for how to manage traffic on such roads. When it's not safe for vehicles to pass, he encourages people to "take the lane," meaning move into the lane instead of hugging its shoulder to make themselves obvious and send a message to motorists.

A state law that took effect Jan. 1 requires motorists to keep a "reasonable and prudent distance" from cyclists. That should be no closer than three feet if traveling 30 mph or slower, with an additional foot of space given for every 10 mph faster. That law is now incorporated in driver training manuals.

Dave Topham, director of the Bike-Walk Alliance of New Hampshire who advocates for bike safety, said cyclists must follow the rules, too. He said, he doesn't like to use the word "accident" to describe collisions between cars and bikes.

"Crashes are avoidable if people follow the law," he said.